1. Field of the Invention
The present invention relates to a method, system, and article of manufacture for copying data from a first cluster to a second cluster to reassign storage areas from the first cluster to the second cluster.
2. Description of the Related Art
In a dual cluster system, each cluster includes a processing complex, cache and non-volatile storage unit (NVS). Each cluster is assigned a plurality of volumes, where volumes may be grouped in Logical Subsystems (LSSs). Data being written to a volume may be stored in the cache of the cluster to which the data is assigned. For cache fast write (CFW), a copy of data is only maintained in the cache of the cluster to which the data is assigned. CFW data is not protected from a reboot or power loss, and may comprise easily reconstructed data, such as sorted lists, indexes, etc. For Direct Access Storage Device (DASD) fast write (DFW) data, a copy of data in cache is also copied to the NVS of the other cluster to provide a backup copy. DFW data may comprise customer data, which is protected from loss. Sequential Fast Write (SFW) data and modified metadata are data stored in cache and information on the data, such as the track identifier (ID), may be stored in the NVS of the other cluster. In this way, if there is a failure, information on the data storage location of the data that was in cache is preserved.
A failover operation is initiated if one cluster fails or requires service or maintenance. As part of a failover operation, all volumes or LSSs assigned to the removed cluster are reassigned or failovered to the surviving or sole operating cluster. In the event the removed cluster recovers, then a failback to dual mode operation commences to reassign volumes back to the recovered cluster to return to dual cluster mode operations. As part of the failback to dual mode, the first cluster will destage all data in the cache and NVS to the storage. If the destage operation succeeds, then volumes, e.g., LSSs, will be reassigned from the operating single cluster to the recovered cluster to operate in dual mode. If the destage operation fails, then the clusters still operate in single cluster mode where the surviving cluster maintains the assignment of all the volumes. In such case, the recovered cluster remains removed from operations.